GTP (General Packet Radio Service Tunneling Protocol) is a communications protocol that is widely applied between network elements of a GPRS network, for example, applied between an SGSN (Serving GPRS Support Node) and a GGSN (Gateway GPRS Support Node), and GTP will continue to be used in an EPS (Evolved Packet System). GTP is used to forward a signaling message and a service data packet. A network element using the GTP protocol identifies a GTP tunnel by using an IP address, a UDP (User Datagram protocol) port number, and a TEID (Tunnel Endpoint Identifier).
A direct tunnel is one of user plane tunnel modes in a GPRS network and may also be used in an EPS network. An RNC (Radio Network Controller) and a GGSN or an SGW (Serving Gateway) directly establish a user plane tunnel by using the SGW in the EPS network, and uplink and downlink user plane data packets are directly forwarded between the RNC and the GGSN (or the SGW), without the need to pass through an SGSN. When a user terminal is idle, in a direct tunnel mode, the SGSN updates a user plane tunnel on the GGSN (or the SGW) by using a signaling message and establishes a user plane tunnel between the SGSN and the GGSN (or the SGW). When downlink data packets of a user terminal in an idle state are forwarded to the SGSN through a corresponding user plane tunnel, the SGSN initiates a paging process to trigger the user terminal to initiate a service request process, so as to establish a signaling connection and a radio bearer between the user terminal and the network and change the user terminal into a connected state. In the service request process, if the SGSN decides to establish a direct tunnel, the SGSN separately exchanges a signaling message with the RNC and the GGSN (or the SGW) to exchange tunnel endpoint identifiers of the RNC and the GGSN (or the SGW), and establishes a direct tunnel between the RNC and the GGSN (or the SGW). In addition, the service request process may also be actively initiated by the user terminal. A mechanism of the direct tunnel can reduce the number of path hops for forwarding a user plane data packet, thereby reducing a service delay.
However, due to features of some services or terminals, to establish a direct tunnel or to cancel a direct tunnel, the SGSN frequently sends a signaling message to the GGSN or the SGW, which leads to an increase in the number of signaling messages that need to be processed on the GGSN or the SGW and increases signaling load on the GGSN or the SGW.